1. Field of the Invention
The present invention relates to a filler member to be installed in a crankshaft of an engine used for a portable working machine.
2. Description of the Related Art
In a two-stroke engine used in a portable working machine such as a chainsaw, a brush cutter, and a blower, a piston reciprocates in a cylinder by expansion force generated when an air-fuel mixture gas is burned in a combustion chamber after the air-fuel mixture gas in a crank chamber is introduced into the combustion chamber disposed above the cylinder through a scavenging port.
In the crank chamber the crankshaft for converting a reciprocating motion of the piston into a rotary motion is housed. On the crankshaft a crank journal rotating about an axis thereof and a crank web protruding from the crank journal in a diametrical direction of the crank journal are formed.
The crank web includes an arm linearly extending, a weight more extending in both rotational direction of the arm than a width of the arm. A tip of the arm is connected to the piston through a connecting rod to rotate the crankshaft synchronously with the reciprocating motion of the piston.
There is a conventional crankshaft having bodies disposed on both sides of the arm in the rotational direction of the arm to cause the crank web and the bodies to have a disk shape. More specifically, an insertion member on which two bodies are formed is installed in the crank web, and the insertion member is fixed to the crank web by surrounding outer circumferences of the crank web and the both bodies with an annular member (see JP 4392224).
This configuration increases a compression ratio (primary compression ratio) of the air-fuel mixture gas in the crank chamber because a volume of the crank chamber is decreased because the both bodies are installed in the crank chamber. Accordingly, this configuration may provide improvement in increase in an output performance and an acceleration performance, and decrease (emission reduction) in exhausting air contaminants such as HC (hydrocarbon).
In the configuration of the conventional crankshaft in which an annular member surrounds the outer circumferences of the crank web and both the bodies, it was necessary to prevent the annular member from shifting by forming a channel in outer surfaces of the crank web and both the bodies and inserting the annular member into the channel. Therefore, this configuration requires a process of the crank web and a fixing operation of the annular member becomes complicated.